USGS Mendenhall Postdoctoral Research Program - FY14 Research Opportunity
14-9. From Local to Landscape: Harmonics and Synthesis of Phenology and Climate Data Across Spatial
and Temporal Scales
The need to understand local patterns of recurring seasonal biological events (phenology) in the context of environmental
variation at regional to continental scales has emerged as a priority for natural resource management, especially in
response to global climate change. Whereas observations of organismal (ground-based, or in situ) phenophases occur at
discrete points, natural resource management decisions are made within the context of landscapes. Although landscapelevel remotely-sensed land surface phenology (LSP)—in the form of time-series vegetation indices (e.g., NDVI, EVI) and
derivatives known as phenometrics—is a powerful tool to understand the response of a landscape to the sum of its
environmental conditions, the linkages between LSP, ground-based observations of phenology, and environmental
forcings, such as climate, remain poorly understood. Spatially extensive, ground-based, standardized datasets being
collected by USA-NPN, NEON, NPS, NWRS, and other ground-based observing systems, coupled with continental
biophysical observation systems managed by NASA, NOAA and others, represent a rapidly emerging resource for the
development of techniques to cross-walk and identify linkages between LSP captured by satellites and phenological
activity observed on the ground.
The continent-wide coverage and frequent repeat times of LSP (e.g., from MODIS), the national network of historic
meteorological data, and the more recent ground-based phenophase observations have the potential to be integrated
together to understand both pattern and process that can be translated broadly across the landscape. For example, USGS
scientists are exploring Fourier harmonics to derive and compare the harmonics of LSP and of ground-based (in-situ)
observations (see figure). Because Fourier analysis characterizes the shape of the complex curve, rather than the absolute
Magnitude
Fourier
NDVI or leaf
1st
Frequency
Phase
Observations
Example of Fourier harmonics
analysis of 2011 time series of
in-situ deciduous tree leaf
phenophases observation data
and MODIS-derived NDVI
data for three USA-NPN
observation stations in
California, Colorado and Idaho.
Top row, annual profile of
observations; bottom row,
Fourier first frequency cosine
wave fitted to profiles. The
vertical dashed lines facilitate
comparison of the two datasets.
values, it enables comparison of response curves derived for any number of variables, such as LSP, climate (temperature
and precipitation) and ground-based (in-situ) observations.
We seek proposals (due September 20, 2013 via the USGS Mendenhall post-doctoral program webpage) to explicitly use
one or more methods to characterize the shape of complex curves and to identify resonance and relationships among
landscape and local phenology and environmental time series. The successful candidate will identify a suite of datasets
with appropriate spatial and temporal scales, including in situ phenophase data (e.g., from the USA-NPN database or other
known datasets), LSP data and/or associated phenometrics, and climate data. The optimal proposal would also identify a
potential application of the integrated and synthesized analysis to maximize the potential that the research will be relevant
to science-informed decision-making on Department of Interior lands. Opportunities for applications include using the
metrics to quantify the impact of restoration activities; predict optimal timing for treatment of invasive vegetation; predict
optimal time to inventory birds, flowers, mammals; and quantify the spatially explicit predictability of interannual
ecosystem dynamics to assess the reliability of ecosystem services provisioning.
Duty Station: Co-located with a research advisor as determined by details of the proposal and candidate preference;
options include Tucson, AZ; Sioux Falls, SD; Flagstaff, AZ. Areas of Ph.D.: Geography, biology, environmental science,
climatology, ecology, GIS/remote sensing science, spatial modeling, or related fields.
Further information: found at http://geology.usgs.gov/postdoc/opps/2014/14-9 Wallace.htm and by contacting research
advisors Cynthia Wallace, (520) 670-5589, cwallace@usgs.gov; Jake F. Weltzin, (520) 626-3821, jweltzin@usgs.gov;
Joel B. Sankey, (928) 556-7289, jsankey@usgs.gov; Jesslyn F. Brown, (605) 594-6003, jfbrown@usgs.gov
Mendenhall Program: information and FAQs are available at: http://geology.usgs.gov/postdoc/